1. Technical Field
The following description relates to one or more image processing techniques to clearly differentiate two areas in a single-hue image including a plurality of areas expressed by the same hue or achromatic color.
2. Related Art
There is disclosed in Japanese Patent Provisional Publication No. 2005-79750 (see paragraph 0014 or FIG. 1) a technique to extract a character highlighted in a color image before converting the color image into a monochrome image and express the extracted character as a character of the maximum density or an outline character, so as to solve a problem that it is hard to discriminate, from a background, the extracted character that has almost the same density as that of the background in the monochrome image.
However, the above technique, disclosed in Japanese Patent Provisional Publication No. 2005-79750, can be applied to a character that is previously highlighted in the color image. Therefore, for example, when adjacent areas in a circle graph have their respective different hues and yet the same brightness (density) in the original color image, even though using the above technique, it is impossible to differentiate the adjacent areas in the monochrome image.